22WMR is hardly an efficient pistol caliber, most of the time. The exception is when it’s used with CCI Gold Dots or other loads made just for short barrels. Then it becomes usable, if not ideal, for self-defense.
The plus side is that 22WMR has minimal recoil compared to 38 Special. So does 32H&R Magnum, but 22WMR ammo is far, far more available and quite a bit less expensive. So this chambering splits the difference between the ideal practice and the useful defensive loads. For somebody who only owns one revolver, that can be a useful compromise.